Conventionally, two or more storage batteries, such as a lead storage battery and a lithium ion storage battery, may be used together in a battery system mounted on a movable body, such as a vehicle, a vessel, an airplane, and so on. If these storage batteries are deteriorated by long-term use, electromotive force is reduced and output is reduced. For this reason, it is necessary to determine deterioration degree of these storage batteries and to replace a storage battery which has reached an end of lifetime (assumed usable period).
Although a technology of detecting characteristics (voltage, current, impedance, or the like) of a storage battery and determining deterioration of the storage battery based on the detected value is known, there is a ease that cost of a battery system is increased by preparing a detector which detects characteristics of a storage battery in both of the lead storage battery and the lithium ion storage battery.